Method for the prevention of corrosion in steel digesters



Patented Dec. 15, 1925.

UNITED STATES 1,566,118 PATENT OFFICE.

FRANCIS GEORGE BAWLHVG, OF MADISON, WISCONSIN, DEDICATED, BY IESNE AS- SIGNIIR'IS, TO THE CITIZENS OF THE UNITED STATES OF AMERICA.

IE'IEOD FOR THE PREVENTION OF CORROSION IN STEEL DIGES'IERS.

Io Drawing.

. lpplication filed larch 21, 1925. Serial No. 17,370.

(Gun-mums: m new or :nacn a, ms; 22 sum. 1., 625.)

To all whom it may corwem:

Beit known that -I, FRANCIS GEORGE Rawnme, a citizen of the United States of America, and an employee of the Department of A riculture, residing in the city of Madison, 7 ofiice address is Madison, Wisconsin, have invented a new and Improved Method for the Prevention of Corrosion in Steel Digest- 10 'ers, of which the following is a specification. This application is made under the act of March 3, 1883, chapter 143 (22 Stat. 625), and the invention herein described and claimed may be used by the Government of the United States, its officers and employees,

and by any person in the United States without the payment to me of any royalty thereon. I hereby dedicate the same to the free use of the Government and the people of the United States.

Hitherto, in the processes of manufactul ing paper pulp from wood, by cooking such material with an aqueous solution of sodium 5 of caustic soda on the wood, an undesirable quality of pulp is produced. There is also a limit to the'amount of caustic soda, which may be added to the digester, as. an excess prevents the proper production of pulp from 40 .the wood by means of the sodium sulphite.

The use of caustic soda solution is not successful in preventing the corrosion of the steel digesting vessel, .when used in such \quantity that a pulp is produced having the quality of one made by cooking wood with sodium sulphite alone.

This invention relates to the addition of .thesodium salts of a polybasic acid, which is not strongly ionize in solution, to the solution of sodium sulphite used for cooking the wood, with thesubsequent addition of as tis $91121 x qlut u g he act a ateof Wisconsin, whose postperiod of cooking. When proper amounts of the sodium salt of the polybasic acid-and of caustic soda are used, no free caustic soda is present in the cooking liquor at any time, but the condition of alkalinity of the cookmg liquid is sufliciently strong, that the latter does not'corrode' the steel vessel or digester in which the cooking is'done.

According to my present invention, wood is boiled under pressure with an aqueous solution of sodium sulphite, containin the sodium salt of a weakly ionized poly asic acid (for example, sodium carbonate, sodium silicate, sodium borate, sodium phosphate, and other with the subsequent addition to the digester, during the period of digestion, of an aqueous solution of caustic soda, at such a rate that the digesting solution remains alkaline in reaction, yet does not contain caustic soda in sufficient amount to alter the quality of the resulting pulp, from that of a pulp prepared from wood by means of a sodium sulphite solution.

It is to be understood that the proportion of sodium sulphite to the, sodium salt of the weakly ionized polybasic acid may be varied between Wide limits and that the caustic soda solution may be added continuously or intermittently to the digester during the period of cooking; also, that the term sodium salt of a weakly ionized polybasic acid is not tobe limited to the four salts mentioned, and

that one or more of such salts may be used in the same solution of sodium sulphite.

Having thus described my invention in above specification, I desire to' secure by Letters Patent the following claims:

1. The process of adding the sodium salt of a weakly ionized polybasic acid to an aqueous solution of sodium sulphite to be used for the pulping of wood, in a steel vessel, with the subsequent addition of a solution of caustic soda to the contents of the steel vessel during the period of cooking, for the purpose of preventing corrosion of'the said vessel. r

2. The process of adding a mixture of the sodium salts of weakly ionized olybasic acids to an aqueous solution of so ium sulphite, to be used for the pulping of wood,

m a steel vessel, with the subsequent additents of the steel vessel during the period of cooking, for the purpose of preventing the corrosion of the said vessel.

3. The process of adding sodium carbonin a steel vessel, with the subsequent addition of a solution of caustic soda, to the contents of the steel vessel, during the period of cooking, for the purpose of preventing the corro- 10 sion of the said vesseL December 26th, 1924.

FRANCIS GEORGE RAWLING. 

